The present invention relates to an acoustic transformer for coupling energy through a non-piezoelectric medium.
There are many, applications in which it is desirable to sense conditions on one side of an isolating medium and transmit them to the other side of the medium without physically penetrating the medium itself. For example, it is desirable to be able to sense the hydrostatic pressure on the hull of a ship or submarine without compromising the integrity of the hull itself which would result by the installation of through-hull pressure transducers.
Transmission of power and/or information across a medium such as a ship's hull without physically penetrating the medium suggests the use of a transmitting means other than electricity, such as an acoustic wave. Such a means would require the use of some type of acoustic transceiver on one side of the barrier and a corresponding transceiver on the other. Such transceivers may involve the use of piezoelectric transducers. The combination of piezoelectric transceivers and associated circuitry form an acoustic transformer. Transformers with a piezo-electric core couple electrical energy from the primary to the secondary with high efficiency while inherently providing galvanic isolation between primary and secondary.
The principal of operation of such transformers involves the conversion of electrical energy to acoustic energy in the primary of the transformer and the coupling of the latter energy to the secondary of the transformer where the acoustic energy in the secondary is converted to electrical energy. The acoustically conductive and electrically non-conductive piezo-ceramic material takes the place of the conventional transformer's magnetically and electrically conductive core. Acoustic transformers may be of a variety of shapes including toroidal, a thin elongated rectangular wafer, disc-shaped, etc. Moreover, the leads and conductive pads may be placed in any number of configurations.
Depending upon the shape of the material and the configuration of the conductive pads one can achieve a variety of input and output impedances, frequency and voltage step-up. Piezoelectic transformers achieve efficiencies of about 90% at or near resonance. At resonance a square wave input will produce a sinusoidal output voltage and current at the resonance frequency. Consequently, operation is generally selected to be at resonance. Typically a resonator sends acoustical energy along the material at about 150 kHz. At the other end, an identical resonator receives the acoustical energy and converts it back to electrical energy. After rectification and filtering, the electrical energy may be used to power an amplifier or other circuit.
Unfortunately, known piezoelectric transformers utilize a single core of piezoceramic material. The problem becomes how to utilize such a structure across a medium which cannot be penetrated.
Accordingly, it is an object of the present invention to provide an improved method and apparatus for transmitting energy across a medium without penetrating the medium.